1. Field of the Invention
The present invention relates to a fuel injection apparatus, which has a common rail and performs a feedback control operation for approximating an actual rail pressure of the common rail to a target rail pressure, and further relates to a subject device control system, which performs a feedback control operation for approximating an output result of a subject device to a target output.
2. Description of Related Art
The background art of the invention will be described with reference to a fuel injection apparatus having a common rail (or simply referred to as a common rail type fuel injection apparatus).
In the common rail type fuel injection apparatus, high pressure fuel is supplied to the common rail from a high pressure pump, which is installed in a supply pump arrangement, and the high pressure fuel, which is accumulated in the common rail, is injected into cylinders of an internal combustion engine through injectors.
A rail pressure in the common rail corresponds to an injection fuel pressure of the injectors and is adjusted by an intake metering valve, which is installed in the supply pump arrangement. When a degree of opening of the intake metering valve is adjusted, the rail pressure of the common rail is controlled and is adjusted.
The degree of opening of the intake metering valve is corrected through feedback (hereinafter, the feedback will be denoted as “F/B”) in such a manner that an actual rail pressure, which is measured through a rail pressure sensor, coincides with a target rail pressure, which is computed based on an operational state of the internal combustion engine (hereinafter, simply referred to as an engine). For example, Japanese Unexamined Patent Publication No. 2000-282929 discloses this technique.
Here, the common rail type fuel injection apparatus is operated in such a manner that the fuel is always filled in the system, which includes the supply pump arrangement.
However, when the remaining amount of fuel in the fuel tank becomes relatively small or when the air is not sufficiently removed from the system, the air may possibly enter through an inlet of the supply pump arrangement to cause inclusion of the air in the supply pump arrangement.
When the air enters the supply pump arrangement, the following phenomena occur.
That is, when the air enters the supply pump arrangement, the actual rail pressure of the common rail drops. The drop in the actual rail pressure of the common rail, in turn, causes an integral term of the F/B control to become an excessive integral. Then, this causes the degree of opening of the intake metering valve to become excessively large. Therefore, the opening degree of the intake metering valve becomes its full open degree. Thus, the supply pump arrangement is operated at its full open state with a full pumping command supplied thereto.
When the air, which is entered into the supply pump arrangement, is discharged from the supply pump arrangement to eliminate the inclusion of the air in the supply pump arrangement, the supply pump arrangement outputs the fuel at its maximum capacity due to the presence of the full pumping command. Thus, the actual rail pressure of the common rail is increased to cause overshooting of the actual rail pressure due to the fact that the integral term of the F/B control is a value, which is obtained by adding a current integral term to a previous integral term and thereby does not change rapidly (see the line α in FIG. 1).
As discussed above, when the inclusion of the air in the supply pump arrangement is eliminated, the actual rail pressure could become an abnormally high pressure due to the excessive overshooting.
Furthermore, when the actual rail pressure becomes the abnormally high pressure due to the above reason, a safety device for avoiding the abnormality programmed in an engine control unit (ECU) is operated, so that stalling of the engine or driving of the vehicle in a limp-home mode may disadvantageously occur.